Method and apparatus for making adhesive tapes



C. H. SCHAAR foct. 26, 1965 METHOD AND APPARATUS FOR MAKING ADHESIVETAPES 2 Sheets-Sheet 1 Original Filed Aug. 8. 1960 nmmmmmmnmn man madmanman manana ummm aannam m am Hammam mnmnmnmnmm Dumm mmmmmm Dumm Damm-n nmman mmmmnm Dunno m D WWE Oct. 26, 1965 c. H. scHAAR 3,214,502

METHOD AND APPARATUS FOR MAKING ADHESIVE TAPES Original Filed Aug. 8.1960 2 Sheets-Sheet z United States Patent O 3,214,502 METHD ANDAPPARATUS FR MAKING ADHESIVE TAPES Charles H. Schaar, Chicago, lll.,assignor to The Kendall Company, Boston, Mass., a corporation ofMassachusetts @riginal application Aug. 3, 1960, Ser. No. 48,225, novilliatent No. 3,073,304, dated `lian. 15, 1963. Divided and thisapplication dan. 1'5, 1962, Ser. No. 167,215

13 Claims. (Cl. 264-154) This application is `a division of copendingapplication, Serial No. 48,225, filed on August 8, 1960, now Patent No.3,073,304.

This invention relates to perforated adhesive tapes and to a method ofperforating either the adhesive layer on a tape backing or both theadhesive layer and backing. In particular, this invention relates toperforated thermoplastic polyvinyl pressure-sensitive adhesive tapessuitable for use as surgical and first-aid tape bandages.

Surgical tapes essentially are composed of at least two elements: abacking and a pressure-sensitive adhesive layer thereon. The adhesivelayer is normally in direct covering contact with the skin. The coveredportion of the skin is thus sealed from the atmosphere, the adhesivelayer obstructing the normal evaporation of fluids from the skinsurface, resulting, in some cases, in a macerated skin condition. Insome instances maceration has been known to become so severe thatremoval of the tape is associated with painful pulling off of skin, andeven portions of the flesh below the skin. Maceration has been a problemnot only with tapes having substantially impervious plastic filmbackings, but also with tapes having a more pervious backing, namelywoven fabric or cloth tapes used as surgical or athletic strappingtapes.

In the absence of a satisfactory substitute for the pressure-sensitivetape to bind, or to hold wound dressings to, the body, `an obvious meansof reducing maceration was to perforate either the adhesive layer orboth the adhesive layer and the backing, preferably both in case ofimpervious backings. Printing or transferring the adhesive in apatterned formation on pervious backings, such as fabrics andmicroporous films has also been suggested.

Ideally, the tape should have a large open area to provide maximumventilation or aeration of the skin without substantial sacrifice in thephysical properties of the tape and the protective and covering functionto be served thereby. For a given open area, maximum ventilationuniformly under the tape may be obtained by a substantially uniformdistribution of small holes throughout the tape providing direct openpaths exposing the skin to the atmosphere.

Tapes having the open area distributed amongst a large number of smallholes provide a better covering func tion than tapes having the sameopen area but a lesser number of larger holes. Under conditions ofnormal exposure, the tape with the smaller openings will maintain acleaner and neater appearance, thus offering some psychlologicaltherapeutic advantage to the wearer in maintaining a cleaner appearingwound site. Preferably, the openings should be no smaller than thatequivalent in area to a circular opening having a diameter substantiallyless than about l mils and no larger than about 60 mils. Openings inthis size range having substantially straight, non-tortuous paths ofcommunication with the skin and the atmosphere provide adequate exposurefor evaporation of moisture from the skin under the perforations.

Pressure-sensitive adhesives exhibit an undersirable tendency to flow.In perforated tapes the adhesive may creep beyond the peripheral edgesof the Openings, sometimes to the extent of completely obstructing theopen- ICC ing. This tendency may be accelerated at elevated temperaturesof steam sterilization, and even at temperatures as low as about 140 F.employed in socalled chemical sterilization cycles. Aside from impairingthe aerability of the tape, the adhesive on the edge of and in theopenings collects dust particles when the bandage is in use and rapidlyacquires an unsightly appearance. Bleeding of the adhesive through theopenings and to the reverse side of the tape may cause undesirably highunwind and picking of the adhesive when the tape is wound in roll form.

Adhesive obstruction of the opening or accumulation of the adhesive atthe very edges of the openings is diiiicult to avoid in known processesof making perforated tapes. Printing of adhesives in a pattern requiringsolvent-thinned adhesives must be carefully controlled to avoidstrikethrough of the adhesive on fabric backings. Transferringprepatterned adhesives onto the matrix of a perforated film withoutcovering the openings therein presents diiiicult problems ofcoordinating the feed of the film to the adhesive pattern on theprinting roll.

Mere mechanical puncturing of an adhesively coated backing isunsatisfactory. This method forms flaps around the puncture in thebacking which may return to their normal position forming a closure. Inaddition, adhesive fragments may adhere to the puncturing needle andtransfer to the reverse side of the tape or the edges of the punctureupon withdrawal thereof. Adherence of ad- 'hesive fragments may beminimized or eliminated by heating the needle to a temperature at whichthe adhesive will be sufficiently flowable to slide from the needle. Theheat of the needle may adversely affect the adhesive; in some casesheating of the adhesive may pyrolyze the adhesive and even the film whenexposed to the atmosphere.

Die cutting operations employed in perforating plastic film backed tapesreduce the strength properties of the tape by reason of the wastefulremoval of material from the tape and also by reason of radial tearsproduced along the edges of the holes by the cutting operation. Thereduction in tensile strength can be tolerated in the area of thebacking over an adhesively secured absorbent gauze pad because the padserves to reinforce this part of the backing. Die-cut perforated tapesusually are limited to the rather large size version of the commercialform of the finger bandage having relatively few number of holes in thetape, less than about per square inch of tape. The adhesive layer ofthese die-cut perforated tapes extends to the peripheral edges of theopenings and may feather-out into t'he openings as explained above.

In general, perforated adhesive tapes of this invention comprise anadhesive layer having openings therein which are in substantial registerwith openings in a thermoplastic film backing, but which are larger thanthe openings in the backing so that the edges thereof are recessed fromthe edges of openings in the backing. More particularly, the openings inthe backing are surrounded by annular grommets formed. on the adhesivelycoated side of the tape, the grommets having surface portions thereofsubstantially flush with a facing sheet on the adhesive side of thetape. The annular grommet-s retain the body of the adhesive layer fromthe edges of the openings in the backing, preventing creep ing of theadhesive tothe edges of the openings and bleed-through into the openingsunder conditions normally encountered in packaging, sterilizing, storageand use. The perforations in the adhesive layer, the perforations in thethermoplastic lilm, and the annular grommets are formed by subjecting animperforate adhesively coated iilm to heat and pressure in discreteareas to melt the adhesive, causing the adhesive to recede from the areaof applied heat and pressure, and to melt the thermoplastic film in theportions from which the adhesive recedes, forming the molten film inraised annular grommets around the film openings. As will be moreparticularly described, the adhesive layer is perforated whilepositioned between the backing and a temporary releasable facing sheet.Included within this invention is a process of perforating an adhesivelayer on a backing under heat and pressure while protecting the adhesivefrom oxidative degradation.

The invention will best be understood by a detailed description withreference to the drawings wherein:

FIGS. l and 2 are enlarged diagrammatic planar views of portions ofperforated adhesive tapes, viewed from the backing side of the tape;

FIG. 3 is a greatly enlarged diagrammatic cross-sectional, partlyperspective view of a portion of the adhesive tape shown in FIG. l, witha portion of the adhesive layer removed, as viewed from the adhesivelycoated side of the tape;

FIG. 4 is a diagrammatic planar View of an adhesive tape bandage made inaccordance with this invention;

FIG. 5 is a cross-sectional View of a portion of the adhesive tape ofFIG. 4, showing a protective facing sheet being stripped therefrom;

FIG. 6 is a schematic drawing of the process of this invention, theapparatus suitable for carrying out this process being diagrammaticallyillustrated; and

FIGS. 7 and 8 are diagrammatic representations of the formation ofperforations in adhesive tape.

Views of tapes 40 from the backing side are set forth in FIGS. 1 and 2merely for the purpose of illustrating two shapes of openings among themany shapes which the openings may assume and two of the many patternsin which the openings may be arranged. As shown in FIGS. l and 2, apolyvinyl film 41 is perforated with openings 42: substantiallyrectangular openings in the tape of FIG. 1 and diamond-shaped openingsin the tape of FIG. 2. The tapes of FIGS. 1 and 2 also differ from eachother in the pattern in which the openings 42 are arranged: the openings42 arranged substantially in straight rows in which the openings arealigned with each other in both longitudinal and transverse directionsof the film 41 in FIG. 1 and in a staggered pattern in FIG. 2. Randompatterns of openings and openings of random size may be employed.Uniform patterns of arrangement and size of the openings are to bepreferred where substantially uniform distribution of the open area isdesirable.

The structure by which the body of the adhesive is retained from theedges of the perforations is diagrammatically illustrated in FIG. 3which is a cross-sectional, partly perspective view of a portion of thetape of FIG. l. When viewed from the adhesive side of the tape, thenovel features of this invention are immediately apparent, particularlywhen the color of the film and adhesive layer are different. Forexample, in the case of flesh colored polyvinylchloride tapes with awhite adhesive coating, flesh colored portions of the film correspondingto the surface designated by the numeral 44 in FIG. 2 are apparent asdistinct halos around each opening 42.

The annular grommets 43 are formed from the film material previouslyoccupying the space represented by the opening 42 in the film 41. Eachof the openings 42 is surrounded by a grommet formation 43, comprisingan interior wall 45, the surface 44, and an exterior wall 46. As viewedin FIG. 3, the interior wall 4S extends above the plane of the portions48 of the matrix of the film coated with the pressure-sensitive adhesivelayer 49 and terminates in the substantially horizontal planar surtace44 forming an inner peripheral edge defining the perforation on theadhesive side of the film 41. The surface 44 terminates along an outerperipheral edge 47 spaced from said inner peripheral edge in theexterior rounded by the interior wall 56 of the grommet.

wall 46 which extends downwardly, as viewed in FIG. 2, to the coatedmatrix portion 48 and merging therewith. As formed in the process to bedescribed, the face of the grommet 43 represented by the surface 44 issubstantially planar and substantially coplanar with the plane of theportion of the adhesive layer immediately surrounding the grommets.

The -outer peripheral edge 47 slightly overhangs the exterior wall 46functioning as a retaining lip or rim for the adhesive layer 49.

The adhesive layer 49 extends into direct abutment with the exteriorwalls 46. These walls serve to retain the adhesive in position away fromthe peripheral edge of the opening 42 and protectvely cover theperipheral surface of the edges of the adhesive layer around thegrommets. The overhanging lip or rim at the outer peripheral edge 47 notonly helps to prevent adhesive creep but also helps to preventdelamination of the adhesive when stripping releasable facing sheetsfrom the adhesive layer.

FIG. 4 illustrates a finger-type adhesive bandage 50 wherein anabsorbent pad 54 is positioned substantially medially on a perforatedtape of this invention secured to the adhesive layer 51. The circularopenings 52 are surrounded by the grommets 53 (shown by heavy lines inFIG. 4) extending through the adhesive layer.

In accordance with the requirements of the U.S. Pharmacopeia bandages ofthe type shown in FIG. 4 must be faced with a protective facing sheetand sterilized. FIG. 5 illustrates in detail, exaggerated for purposesof clarity, the adhesive retention advantage of the grommets and inparticular grommets having a retaining rim at the outer peripheral edgethereof. Referring to FIG. 5, the opening 52 in the backing 55 is sur-The adhesive layer 51 extends into abutment with the exterior wall 57and up to the jutting rim forming the outer peripheral edge 58. Thenumeral 59 designates a facing sheet in the process of being strippedfrom the adhesive layer 51 as it is passing over and past the outerperipheral edge 58. The adhesive layer is in adherent contact not onlywith the matrix portions of the film but also with the substantiallyvertical exterior wall 57 and the overhanging rim at edge 58.Delamination by splitting of the adhesive layer beginning at the edgesof the perforations is resisted by the adhesive forces at these portionsof the film and grommets.

In the case of polyvinylchloride films the surface 53 of the grommet maybe slightly irregular after sterilization and not as flat as prior tosterilization. The edges of the grommet however remain substantiallyflush with the surface of the adhesive layer 51.

Perforated thermoplastic film backed pressure-sensitive' adhesive tapeshave been made in accordance with this invention by the processschematically illustrated in FIG. 6. In this process a faced tape issubjected to pressure in discrete areas thereof pressing the faced tapefrom the film side against a heated surface. Under the conditions ofheat and pressure the adhesive layer and film melt or are renderedfiowable and recede from the areas of applied pressure thereby producingopenings therein.

Referring specifically to FIG. 6, the numeral 60 designates a smoothmetal roll, heated in any appropriate manner. Roll 61 is a knurled metalroll, the surface of which contains raised protuberances or bosses 62.The surface 63 of each of the bosses 62 is substantially flat and mayhave a configuration corresponding to the shape of the openings desired.The numeral 64 designates the walls of the bosses 62. Rolls 60 and 61are positioned with respect to each other to subject a tape passingthrough the nip between the rolls to pressure. Roll 61 is driven androll 60 is rotatable, rotating by frictional engagement with the facedtape 65 passing through the nip. The direction of rotation is indicatedby the arrows.

The faced tape 65 is placed upon a back-up sheet 66 with the filmbacking against the back-up sheet. The tape 65 and back-up sheet 66 areintroduced into the nip between the rolls 60 and 61. The composite ofthe backing 66 and faced tape 65 are momentarily subjected to heat andpressure in discrete areas between the surface of the roll 60 and thesurfaces 63 of the bosses 62. Depending upon the conditions employed,either the adhesive layer alone can be perforated in these discreteareas of applied pressure or both the adhesive layer and thermoplasticfilm backing can be perforated.

Reference to FIGS. 7 and 8 illustrates diagrammatical- 1y the formationof the perforations in the tapes shown in FIGS. 1-3 at the nip betweenrolls 60 and 61. The faced adhesive tape generally designated by thenumeral 65 comprises a thermoplastic film 41, for example, apolyvinylchloride film, coated with a pressure-sensitive adhesive layer49. The adhesive layer 49 is covered with a thin facing sheet 67, forexample, cellophane film. A back-up sheet 66, for example, ordinarynewsprint paper sheet, is placed against the polyvinyl film.

As the boss 62 engages the composite of the faced tape 65 and theback-up sheet 66, the cellophane facing 67 is pressed against thesurface of the roll 60. The adhesive layer directly underneath thefacing sheet, as viewed in FIG. 7, is melted and flows laterally betweenthe film 41 and the cellophane facing sheet 67 radially away from theareas subjected to pressure between the roll 60 and the boss 62. Undercontinued pressure the film 41 is projected into the space created bythe melted and recessed adhesive, the outer surface of that portion ofthe film turning in toward the adhesive layer to form the surface of anembossed depression in the film. As schematically illustrated at thisstage in FIG. 7, only the adhesive layer is perforated, the openingtherein corresponding in general to the configuration of the surface ofthe boss 62.

Under sufficient pressure forcing rolls 60 and 61 toward each otherprojected portions of the film are heated against the surface of thecellophane facing sheet to a molten state causing the molten film toshift laterally between the facing sheet 67 and back-up sheet 66. Asshown in FIG. 8 the molten projected film portion is displaced from thearea of applied pressure and is accumulated in a solidified annulargrommet 43 formed on the adhesive side of the tape with the externalwalls 46 and the jutting peripheral edge 47 abutting the adhesive layer,as previously described in reference to FIG. 3.

Depressions 68 in the adhesive layer 49 may occur, as shown in FIGS. 7and 8, outlining what appears to be adhesive grommets or annular ringsaround the annular film grommets 43. The adhesive layer immediatelyadjacent to the grommets and the face of the grommets 4 3 are in flushcontact with the facing sheet 67. These depressions may disappear uponheating at about 140 F. during chemical sterilization of the faced tape.Apparently when heated the adhesive layer becomes suficiently flowableto level out, the adhesive generally conforming to the surface of thefacing sheet. These depressions do not always occur in the adhesive.

During the perforation step under applied pressure and heat the moltenportion of the adhesive layer is protected against exposure to theatmosphere by the mperforate facing sheet 67. The facing sheet also actsas a molding surface, supported by the roll 60, against which theadhesive and film may be displaced radially from the zones of appliedpressure and heat. The facing sheet must be substantially dimensionallystable when subjected to the pressure and heat. The facing sheet must bestrippable from the adhesive layer. Wettable cellophane film issatisfactory as a facing sheet and can withstand temperatures as high asabout 560 F. which may be employed in the process of perforatingpolyvinyl film pressure-sensitive adhesive tapes.

The temperature of the heated smooth roll 60 and the pressure betweenthe roll 60 and the roll 61 depends upon the tape composition, the rateat which the tape passes between the rolls which determines dwell timeof the applied pressure and temperature, the thermal conductivity of thefacing sheet, and the thermal conductivity ofthe bosses 62 or the bosses62 covered by a back-up sheet. As to tape composition,pressure-sensitive adhesives are soft, semi-solid materials at ordinaryroom temperatures. The application of pressure alone can force theadhesive to shift away from the area of applied pressure. The rate atwhich the adhesive is displaced is accelerated at elevated temperatures.Accordingly, only moderate temperatures and pressures need be employedif perforation of the adhesive layer alone is desired on either film orfabric backings.

Interestingly, temperatures and pressures suiiicient to perforate both apolyvinyl film and an adhesive layer of a faced tape, when passedthrough the nip between the metal rolls 60 and 61 with a back-up sheetas described in reference to FIGS. 6-8, were insufficient to perforatethe film backing when the back-up sheet was eliminated. Increasing thepressure between the two rolls resulted in thinning of the projectedfilm portion coincident with the opening in the adhesive layer. Anoccasional few of these veil-like thinned projected film portions wereruptured. Still eliminating the back-up sheet, the polyvinyl film tendedto deform and shrink when the roll 61 was heated to the melting point ofthe film.

Based on these observations it was discovered that concentration of thetransmission of heat from the smooth roll 60 in the portions of the tapesubjected to pressure without dissipation of the heat by conductancethrough the metal bosses of the roll 61 produced the perforationsillustrated in the drawings. The use of a back-up sheet providingthermal insulation for the metal bosses is a convenient way of avoidingheat dissipation from the tape and also avoiding unduly hightemperatures for roll 61. Satisfactory results may be obtained bythermally insulating the metal bosses by a coating of low thermallyconductive material, such as oils, greases, and resins. Alternatively,the knurled roll 61 may be made of hard, non-thermoplastic resins havinga thermal conductivity less than Ithat of steel. Metal rolls generallymay be preferred because of their greater resistance to wear.Dissipation of heat may also be minimized by reducing the temperaturedifferential between the heated roll 60 and the knurled roll 61 byheating the knurled roll to a temperature below that at which the filmwill deform as it is passed between the rolls.

These principles of the process which produces the perforated tapes ofthis invention will be illustrated in the following specific examples.

Example 1 A thermoplastic film about 0.002 thick comprisingpolyvinylchloride suitably plasticized with a mixture of a sebacic acidpolyester and epoxidized soybean oil and containing minor amounts ofconventional light and heat stabilizers, fillers, and pigments to imparta flesh color thereto, was coated with the following pressure-sensitiveadhesive from a heptane solution thereof:

Ingredients: Parts by weight Pale crepe rubber 76.5 Tackifier resins78.0 Fillers 70.8 Age resistors 1.6

The tackifier resins were a blend of a glycerol ester of hydrogenatedrosin, dimerized abietic acid and pentaerythritol ester of hydrogenatedrosin, The age resistors were a mixture of polymerized trimethyldihydroquinoline, diorthotolyethylene diamine and a condensation productof acetone and aniline. The plasticized polyvinylchloride film had asoftening point within the range of about 320 7 F. to 345 F. Thepressure-sensitive adhesive layer was about 0.0021 thick.

The adhesive layer was faced with a wettable cellophane sheet about0.001 thick. The cellophane faced tape about three inches wide wasplaced on a back-up sheet about 0.001 to 0.002 thick with the polyvinylbacking against the back-up sheet. This composite of back-up sheet, tapeand facing sheet was introduced into the nip between a smooth metal rolland knurled metal roll in the manner described with reference to FIGURE6.

Both the smooth and knurled metal rolls were about 4 inches long, eachhaving a diameter about 2 inches. The smooth roll was heated internallyby an electrical cartridge heater to a surface temperature of about 420F.

The surface of the other roll was knurled to give foursided projectionsor bosses about 0.017 high, the top surface of each boss having aparallelogram configuration measuring about 0.025 by 0.015. The bosseswere arranged in a staggered pattern. There were about 196 bosses persquare inch of roll surface.

The pressure between the smooth heated roll and the knurled roll wasabout 30 pounds per inch of roll length. The knurled roll was driven byan electric motor, at a speed which drew the back-up sheet, tape andfacing sheet through the nip at about 6.6 feet per mniute. The smoothroll rotated in frictional engagement with the cellophane facing sheet.

Under these conditions the tape was perforated with generallydiamond-shaped openings with the openings arranged in a staggeredpattern in the manner shown in FIG. 2. The paper back-up sheet wasembossed with the diamond pattern. The cellophane facing wassubstantially smooth and not perforated. The perforations in the vinylfilm were surrounded by annular grommets formed on the adhesive side ofthe film. The face of each grommet was substantially flush with theplane of the surface of the adhesive layer immediately adjacent thegrom-l mets. The perforations in adhesive layer were larger than theperforations in the film. Viewed from the reverse side of the tape, theportions of the film along the edges of the openings were neatly turnedinwardly toward the adhesive layer providing a straight non-tortuouspath or channel, free of adhesive and ragged film fragments, directlyfrom the film side of the tape to the adhesive side of the tape. Theinner walls of the opening corresponding to the inner walls 45 and innerwalls 56 shown in FIGS. 3 and 5 tapered slightly toward the adhesiveside of the tape.

Perforated tapes having generally rectangular openings were produced bymeans of a knurled roll wherein the surfaces of the bosses wererectangular, measuring about 0.0025 by 0.0135. The projections wereabout 0.017" high.

Example 2 The same tape of Example 1, faced with the wettablecellophane, was placed upon a back-up sheet of high densitypolyethylene. The back-up sheet was about 0.002 thick. This compositewas introduced into the nip of the smooth roll and the knurled rolldescribed in Example 1, the cellophane facing sheet being placed againstthe smooth roll. The composite of tape, backup and facing sheets passedthrough the nip at about 9 feet per minute under pressure of about 30pounds per inch of roll length at the nip. At the start of theperforating run the surface temperature of the smooth roll was about 470F. and the surface temperature of the bosses was room temperature. Atthe end of about a 100 yard run the surface temperature of the smoothroll was about 445 F. and the temperature of the bosses was about 170 F.Neither the back-up sheet nor the facing sheet was perforated, althoughthe back-up sheet was embossed in the pattern of the knurled roll. Boththe film and the adhesive of the tape were perforated. The structure ofthe tape was the same as described in the previous example and asexplained with reference to the drawings.

Example 3 The same tape of Example 1, faced with wettable cellophane butwithout a back-up sheet was fed into the nip between the two rolls, withthe cellophane facing toward the smooth roll. The pressure at the nipand the rate of feed were the same as in Example 2. The tempertaure ofthe smooth roll was about 475 F. and the temperature of the knurled rollwas at room temperature at the beginning of the run. In the absence of aback-up sheet only the adhesive layer was perforated. The polyvinylbacking was embossed with the impression of the surfaces of the bosses.The portion of the film projected into the opening substantially iiushwith the surface of the adhesive was thinner than the matrix of thefilm.

Example 4 A white thermoplastic film, about 0.0045" thick, comprising acopolymer of vinyl chloride and vinyl acetate (5%) suitably plasticizedwith a mixture of epoxidized soybean oil and a polyester of adipic acidand 2- ethyl-1,3-hexanediol and containing titanium dioxide filler werecoated with a 0.0017 thick layer of a pressuresensitive adhesive havingthe following composition:

Ingredients: Parts by weight Butadiene-styrene rubber (GRS-1022) 56 Palecrepe rubber 16 Tackifier resins 64 Plasticizers 4 to 5 Age resistors4to5 Fillers 13 The tackifier resins consisted of a blend of apolyterpene resin and glycerol ester of hydrogenated rosins. Theplasticizers consisted of a mixture of synthetic beeswax, epoxidizedsoybean oil and a polyester of adipic acid and 2-ethyl1,3hexanediol. Thefillers consisted of a mixture of carbon black and finely dividedsilica. The age resistor mixture included polymerized trimethylhydroquinoline, hydrocarbon substituted diaryl amines, and alkylatedpolyhydroxy phenol.

The adhesive layer was faced with a wettable cellophane sheet about0.001" thick and a high density polyethylene film about 0.002 thick wasplaced on the film backing. This composite was introduced into the nipof the two rolls described in Example 1. The smooth roll was heated to atemperature of 450 F. After a period of operation the surfaces of thebosses were F. Both the adhesive and the lm were perforated at apressure of 35 pounds and a speed of about 10.5 feet per minute at thestated temperature and pressure. The grornmet surfaces of the white filmflush against the cellophane facing sheet were distinctly apparent,contrasting with the black adhesive layer which abutted against theouter walls of the grommets.

Example 5 A 0.001" thick polyethyleneterephthlate film coated with a0.0013 thick layer of the adhesive of Example 4 and faced with wettablecellophane film was placed upon a 0.002 thick high density polyethyleneback-up sheet and inserted in the nip between the smooth and knurledrolls as described in Example 1. The temperatures of these two `rollswere, respectively, 520 F. and F. and rotated at a linear speed of about9 feet per minute at a pressure of about 50 pounds. The adhesive wasrecessed from the perforations in the film and abutted against the wallsof the film grommet. The surface of the film grommet was flush againstthe cellophane facing sheet.

Example 6 A preshrunk flesh-tinted, plasticized thermoplastic filmcomprismg a copolymer of vinylidene chloride and vinyl chloride, about0.002" thick, was coated with a layer of adhesive having the samecomposition as the adhesive of Example 1. The adhesive layer was about0.0018" thick.

The adhesive layer was faced with the wettable cellophane. Two strips ofthis faced tape were placed together, the bottom strip with thecellophane facing placed against the film backing of the top strip. Thebottom strip of faced tape served as the back-up sheet.

The superimposed strips were introduced into the nip of the two rollsdescribed in Example 1, with the cellophane facing sheet of the topstrip toward the surface of the heated smooth roll. The smooth roll washeated to a temperature of about 420 F. After a period of operation, thetemperature of the surfaces of the bosses was about 120 F. The pressurebetween the two rolls was about 30 pounds per inch length of the rolls.The two strips of faced tape were fed through the rolls at a speed ofabout 8 feet per minute. The two strips were separated from each other.Both the adhesive layer and the film backing of the top strip of tapewere perforated. The surfaces of the grommets were flush with thecellophane facing sheet. The openings in the adhesive were larger thanthe openings in the film backing, the adhesive layer abutting againstthe aforedescribed exterior wall of the film grommets.

The adhesive layer of the strip of tape serving as the back-up sheet wasperforated; the vinyl film of this strip of tape was embossed in theareas of the openings of the adhesive layer.

Example 7 A 0.002" thick high density polyethylene film was coated witha 0.0017 thick layer of the adhesive described in Example 4. Theadhesive layer was faced with the wettable cellophane. Two superimposedstrips of this faced tape were introduced into the nip of the two rollsas described in Example 5. The temperatures of the smooth roll and thesurfaces of the bosses were, respectively, about 460 F. and about 160 F.The pressure between the two rolls was about 30 pounds. The superimposedstrips of faced tape were fed through the rolls at a linear speed ofabout 9 feet per minute. Both the adhesive layer and the iilm backing oftop strip of tape were perforated. The surfaces of the grommets wereiiush with the cellophane facing sheet. The openings in the adhesivewere larger than the openings in the film backing, the adhesive layerabutting against the aforedescribed exterior wall of the grommets.

The adhesive layer of the strip of faced tape serving as the back-upsheet was perforated; the polyethylene film of this strip of tape wasembossed in the areas of the openings of the adhesive layer.

A series of other examples were run substituting a variety of materialsfor the back-up sheets of the foregoing examples. Materials whichperformed satisfactorily in sheet form as substitute back-up sheets arecellophane, glassine paper, non-woven fabric, woven fabrics, urethanefoam rubber, soft rubber, and low density polyethylene. Coating themetal surfaces of the bosses with oils and grease resulted inperforation of both the film backing and the adhesive layer. Of all thematerials tried, high density polyethylene sheeting on the order ofabout 1.1 mil thickness is preferred as a material which will helpproduce openings of the kind described in the tape of Example 1. Underthe conditions employed a second strip of tape as the back-up sheet waspreferred for the tapes of Examples and 6. The back-up sheeting employedmust be flexible and comformable to the configuration of the projectionsor bosses, such as on the knurled roll.

For the purpose of specifically illustrating the interdependence oftemperature, pressure and dwell time, the following examples are setforth. The tapes in these examples were the same as the tape ofExample 1. Wettable cellophane was employed as the facing sheet and0.0015" thick high density polyethylene was used as the back-up sheet.The initial and final surface temperatures of the CII rolls are setforth. The pressures given are pressures per inch length of rolls at thenip.

Example 8 Temperature, F.

Roll

Initial i Final Smooth Roll Kuurled Roll Openings were formed in theadhesive; the vinyl film was embossed but not perforated at pressures ashigh as 45 pounds at a rate of speed of 9 to l0 feet per minute.

The adhesive layer was perforated and the film was embossed as inExample 8, at pressures of 40 pounds and a speed of about 10 feet perminute.

Example 10 Temperature, F.

Roll

Initial Final Smooth Roll Knurled Roll Speed and pressure were the sameas in Example 8; adhesive layer was perforated and vinyl backing wasembossed but not perforated.

Example 11 Temperature, F. Roll O Initial Final Smooth Roll Knurled RollSame speed and pressure as Example 8; adhesive layer perforated; portionof lm projected into opening of adhesive layer was very thin, veil-like.Some of the veils were ruptured, forming a ragged edge opening.

Example 12 Temperature, F.

Roll

Initial Final Smooth Roll 500 470 Knurled Roll 50 90 At a pressure ofabout 25 pounds and a rate of feed of about 10.5 feet per minute, theperforations in the adhesive layer were partly blocked by rupturedveil-like thin portions of the film. At 35 pounds pressure and the samespeed the openings were substantially clear of film; at 45 poundspressure and about 10 feet per minute the perforations in the vinyl filmwere smooth-edged.

1 l Example 13 Temperature, F.

Roll

Initial Final Smooth Roll 500 470 Knurled Roll 10U 110 smooth non At 20pounds pressure and a speed of about 10.5 feet per minute thin,veil-like fragments of film obstructed the perforations; at 30 poundspressure and a speed of about 10.5 feet per minute a perforatedstructure as described with reference to the drawings was obtained, theperforations being free of adhesive and film fragments.

Example 14 Temperature, F.

non

Initial i Final Smooth Roll Knurlcd Roll At pounds pressure and speed ofabout 11.5 feet per minute thin, veil-like ruptured portions of the filmremained attached to the inner edge of the grommets in this film. Theseveil-like portions were substantially melted and displaced into grommetformations at about pounds pressure and at a speed of about 11.5 feetper second.

Example 15 Temperature, F. Roll Initial Final 465 Knuiled Roll 225 At apressure of 5 pounds and a speed of about 11.5 feet per minute thin,veil-like ruptured portions of the film remained attached to the inneredge of the grommets. At 15 pounds pressure and substantially the samedwell time distinct well defined openings in the film were formed inaccordance with this invention.

Example 16 Temperature, F.

Roll

Initial i Final Smooth Roll Kuurled Roll At 45 pounds pressure and adwell time corresponding to about 10 feet per minute the film did notbecome perforated. The projected film portion appeared very thin andveil-like. A few of these veil-like portions of the film were ruptured.

Ruptured thin, veil-like portions `of the film remained attached to theinner edge of the grommets in the film forming ragged and irregularopenings at 10 pounds pressure and about 11.5 feet per minute.Completely open perforations of the structure described in accordancewith this invention were obtained at about 15 to 20 pounds pressure andspeed of about 10.5 to 11.5 feet per second.

The heat necessary for melting or rendering the adhesive mass and filmflowable is supplied by the smooth surface of the heated smooth roll.The knurled roll becomes heated by conductance of heat from the smoothroll during the process; however, the temperature of the knurled rolldoes not exceed the temperature which heats adjacent matrix portions ofthe film backing to a temperature which causes deformation or distortionthroughout the tap. The maximum operable temperature of the knurled rolland temperature of the smooth roll depends upon the composition andthickness of the tape, facing sheet, back-up sheet, pressure, dwell timeand may also be influenced by the size and design of the apparatus.

For the apparatus described specifically in Example 1 structures inaccordance with this invention are obtained at smooth roll temperaturesin the range of about 300 F. to about 560 F. and, correspondingly,knurled roll temperatures not exceeding about 240 F. at a pressure ofabout 5 pounds and not less than about 90 F. at a pressure of about 45pounds, at dwell times at the nip corresponding to about a rate of feedat the nip of between 6 to 12 feet per minute. Preferably, theconditions should be chosen so as to operate at the lowest temperatures,pressures and dwell times possible. In all circumstances, however, thesmooth surface must be hotter than the projections or bosses to producethe perforated tape structure of this inventionP since the describedgrommets in the thermoplastic films form toward the hotter surface.

Perforated tapes made in accordance with this invention were made intoadhesive bandages of the type described in the U.S. Pharmacopeia. Thecellophane faced perforated tape was first soaked in water to wet thecellophane, the wetted cellophane being easily removable from theadhesive layer. An absorbent pad was lplaced on 3A by 3 strips of theperforated tape. The exposed adhesive was faced with polyethyleneyfacing sheets, the sheets also covering the pad. The bandages werepackaged in individual paper envelopes of the type described in U.S.Patent 2,924,331 and sterilized. Maceration and discloration of the skinwere substantially less for these perforated tapes than for commerciallyavailable film backed adhesive tapes.

From the foregoing it is apparent that a back-up sheet may be omitted inperforating only the adhesive layer of tapes employing non-thermoplasticbackings, such as fabric backings. A facing sheet, however, serves toprevent oxidative degradation of the adhesive at the elevatedtemperatures employed in the perforation process. The adhesive layer ofcloth tapes, faced with a facing sheet, may also be perforated in the`following described process.

Perforated tapes have also been produced with a knurled roll and smoothroll similar to that illustrated in FIG. 6, while protecting theadhesive layer against oxidative inuences of atmosphere, except that inthis instance the knurled roll was heated to about 470 F. and thecomposite of tape, facing and back-up sheets were fed into the nipbetween the two rolls with the faced adhesive side of the tape facingthe heated projections of the knurled roll. The tape was the same asdescribed in Example 1. The back-up sheet, 0.002 high densitypolyethylene film, was in contact with the smooth roll. Initially thesmooth roll was at room temperature. During the run the smooth rollbecame heated to about F. by transmission of heat from the heatedprojections. At a pressure of about 35 pounds and a speed of about 8feet per minute, both the adhesive layer and the polyvinylchloride filmwere perforated. The film grommets which yformed were substantiallyunderneath the adhesive layer at the edges of the openings. The walls ofthe film grommet terminated in a narrow ridge formation. Since theseridges were formed underneath the adhesive layer they were not tiushwith the cellophane facing sheet. The openings in the adhesive wereslightly larger than the openings in the film backing. The wall of thefilm surrounding the opening tapered from the ridges to a smalleropening at the surface of the film against which the back-up sheet wasplaced. Neither the cellophane facing sheet nor the polyethylene back-upsheet were perforated.

What is claimed is:

1. The method of perforating the adhesive layer of an adhesive tape,said tape comprising a liexible backing and a coating of apressure-sensitive adhesive layer, said adhesive layer faced with areleasable facing sheet, cornprising: subjecting portions of saidadhesive layer to heat and pressure rendering the adhesive portionsflowable between said backing and facing sheet at the areas of appliedpressure and displacing the flowable portions of the adhesive laterallybetween said backing and sai-d facing sheet radially from the areas ofapplied pressure; and accumulating said portions of the adhesive in thelayer around the areas of applied pressure.

2. The method of perforating an adhesive tape, said tape comprising athermoplastic film backing and a coating of a pressure-sensitiveadhesive layer, said adhesive layer faced with a releasable facingsheet, comprising: subjecting discrete areas of said adhesive tape toheat and pressure rendering the adhesive portions owable between saidbacking and facing sheet at said discrete areas of applied pressure and`displacing the flowable portions of the adhesive laterally between saidbacking and said facing sheet radially from the areas of appliedpressure to form openings in said layer; accumulating said moltenportions of the adhesive in the layer around the areas of appliedpressure; projecting the portions of the backing coincident with saidareas into the openings created by the displaced adhesive portionsagainst the facing sheet under applied pressure; continuing applicationof heat and pressure rendering the projected film portions fiowableagainst the facing sheet and displacing the film portions laterallyagainst the surface of the facing sheet radially from said areas ofapplied pressure to form openings in said film coincident with theopenings in the adhesive layer; and accumulating the liowable displacedfilm portions in a thickened grommet formation around each of saiddiscrete areas in direct side-by-side abutment with said adhesive layer.

3. The method of perforating the adhesive layer of an adhesive tape,said tape comprising a liexible backing and a coating of apressure-sensitive adhesive layer, said adhesive layer faced with areleasable facing sheet, comprising: heating portions of said adhesivelayer to a molten state at discrete areas under applied pressure betweensaid backing and said facing sheet; displacing the molten portions ofthe adhesive laterally between said backing vand said facing sheetradially from the areas of applied pressure; and accumulating saidmolten portions of the adhesive in the layer around the areas of-applied pressure.

4. The method of perforating an adhesive tape, said tape comprisingthermoplastic film backing and a coating of a pressure-sensitiveadhesive layer, said adhesive layer faced with a releasable facingsheet, comprising the steps of: heating portions of said adhesive layerto a molten state at discrete areas under applied pressure between saidbacking and facing sheet; displacing the molten portions of the adhesivelaterally between said backing and said facing sheet radially from theareas of applied pressure to form openings in said layer; accumu--lating said molten portions of the adhesive in the layer around theareas of applied pressure; projecting the portions of said backingcoincident with said areas into the openings created by the displacedadhesive portions against the facing sheet under applied pressure;heating the projected film portions to a molten state at said areasunder applied pressure; displacing said molten film 14 portionslaterally against the surface of the facing sheet radially from saidareas of applied pressure to form openings in said film, andaccumulating the molten displaced film portions in a thickened grommetformation -around each of said areas of applied pressure in directside-byside abutment with said adhesive layer.

5. The method of perforating an adhesive tape, said tape comprising athermoplastic film backing and a coating of a pressure-sensitiveadhesive layer, said adhesive layer faced with a releasable facingsheet, comprising: subjecting discrete areas of said adhesive tape toheat and pressure rendering the adhesive portions fiowable between saidbacking and facing sheet at said discrete areas of applied pressure anddisplacing the flowable portions of the adhesive laterally between saidbacking and said facing sheet radially from the areas of appliedpressure to form openings in said layer; accumulating said flowableportions of the adhesive in the layer around the areas of appliedpressure; continuing application -of heat and pressure rendering thefilm portions owable at said dicrete areas and displacing said filmportions radially from said areas of applied pressure to form openingsin said film coincident with the openings in the adhesive layer; andaccumulating the displaced film portions in a thickened grommetformation around each of said discrete areas.

6. The method of claim 5 wherein said tape is interposed between saidfacing sheet in Contact with the adhesive layer and a fiexible back-upsheet against said film backing while being subjected to said heat andpressure.

7. The method of perforating the adhesive layer of an Vadhesive tape,said tape c-omprising a flexible backing and a pressure-sensitiveadhesive layer thereon, said adhesive layer faced with a releasablefacing sheet, comprising the steps of: passing the faced tape through anip between a heated smooth surface and projections having end surfacesfacing said smooth surface, said tape positioned in `said nip with thefacing sheet in contact with said smooth surface; applying pressure todiscrete areas of said tape corresponding to the end surfaces of saidprojections by compressing the tape at the nip between said smoothsurface and said end surfaces; melting the portions of said adhesivelayer at said discrete areas under pressure by conductance of 4heatthereto from said heated smooth surface; and displacing the moltenportions of adhesive layer laterally between said facing and backingradially from said discrete areas -by the continued application ofpressure to form performations in said adhesive layer.

8. The method of perforating an adhesive tape, said tape comprising athermoplastic film backing and a coating of a pressure-sensitive layerthereon, said adhesive layer faced with a releasable facing sheet,comprising the steps of: passing the faced tape into a nip between aheated smooth surface and projections having end surfaces facing saidsmooth surface, said tape positioned in said nip with the facing sheetin contact with said smooth surface; applying pressure to discrete areasof said tape corresponding to the end surfaces of said projections bycompressing the tape at the nip between said smooth surface and said endsurfaces; melting the portions of said adhesive layer and backing atsaid discrete areas by conductance of heat thereto from said heatedsmooth surface; and displacing the molten portions of said adhesivelayer and backing laterally along the plane of said facing sheetradially from said discrete areas by continuing the application ofpressure thereto to form perforations in said adhesive layer and saidbacking.

9. The method of perforating an adhesive tape, said tape comprising athermoplastic film backing and a coating of a pressure-sensitiveadhesive layer thereon, said adhesive layer faced with a releasablefacing sheet, comprising the steps of passing the tape into a nipbetween a heated smooth surface and projections having end surfacesfacing said smooth surface, said tape positioned in said nip with thefacing sheet in contact with said smooth 15 surface; heating said smoothsurface to a temperature at least equal to the temperature at which saidbacking is rendered owable under an applied pressure; applying pressureto discrete areas of said tape corresponding to the end surfaces of saidprojections by compressing the tape at the nip between said smoothsurface and said end surfaces; rendering the portions of said adhesivelayer and backing iiowable at said discrete areas by conductance of heatthereto from said smooth surface; and displacing said portions of theadhesive layer and backing radially from said discrete areas bycontinuing the application of pressure thereto to form perforations insaid adhesive layer and said backing.

10. The method of claim 8 wherein said tape is interposed between saidfacing sheet in contact with the adhesive layer and a flexible back-upsheet against said film backing while being subjected to heat andpressure.

11. The method of claim 9 wherein said tape is interposed between saidfacing sheet in contact with the adhesive layer and a flexible back-upsheet against said film backing while being subjected to heat andpressure.

12. The method of perforating an adhesive tape, said tape comprising athermoplastic film backing and a coating of a pressure-sensitiveadhesive layer thereon, said adhesive layer faced with a releasablefacing sheet, comprising the steps of: passing the tape into a nipbetween a smooth surface and heated projections having end surfacesfacing said smooth surface, said tape positioned in said nip with thefacing sheet in contact with said end surfaces; heating said projectionsto a temperature at least equal to the temperature at which said backingis rendered tiowable under an applied pressure; applying pressure todiscrete areas of said tape corresponding to the end surfaces of saidprojections by compressing the tape at the nip between said smoothsurface and said end surfaces; rendering the portions of said adhesivelayer and backing flowable at said discrete areas by conductance of heatthereto from said end surfaces; and displacing said portions of saidadhesive layer and backing radially from said discrete areas bycontinuing the application of pressure thereto to form perforations insaid adhesive layer and said backing.

13. An apparatus for perforating pressure-sensitive adhesive tapecomprising: a rotatable first roll and a rotatable pattern rollpositioned to form a nip therebetween for compression and passage ofpressure-sensitive adhesive tape therethrough, said first roll having asmooth circumferential surface, said pattern roll having a plurality ofbosses thereon isolated from each other by depressed areas of said rollaround each of said bosses the end surfaces of which form discontinuousisolated nips with the smooth surface of said first roll at aternperature higher than the temperature of the end surfaces of thebosses; driving means for rotating said pattern roll; and a releasesheet positioned between said first roll and said pattern roll forpassage therebetween with said adhesive tape providing a surface againstwhich discrete areas of the adhesive under compression at said isolatednips are displaced radially from said nips to provide discrete openingstherein.

References Cited by the Examiner UNITED STATES PATENTS 1,921,456 8/33Delaney 18--10 2,582,294 1/52 Stober 18--10 XR 2,689,379 9/54 Nissel.

2,704,049 3/55 Vogt 83-346 2,817,596 12/57 Schur 117-4 2,822,286 2/58Vogt 117-4 2,928,124 3/60 Hugger 18-10 FOREIGN PATENTS 1,079,767 4/60Germany.

876,086 8/61 Great Britain.

ROBERT F. WHITE, Primary Examiner.

MICHAEL V. BRINDISI, ALEXANDER H. BROD- MERKEL, Examiners.

1. THE METHOD OF PERFORATING THE ADHESIVE LAYER OF AN ADHESIVE TAPE,SAID TAPE COMPRISING A FLEXIBLE BACKING AND A COATING OF APRESSURE-SENSITIVE ADHESIVE LAYER, SAID ADHESIVE LAYER FACED WITH ARELEASABLE FACING SHEET, COMPRISING: SUBJECTING PORTIONS OF SAIDADHESIVE LAYER TO HEAT AND PRESSURE RENDERING THE ADHESIVE PORTIONSFLOWABLE BETWEEN SAID BACKING AND FACING SHEET AT THE AREAS OF APPLIEDPRESSURE AND DISPLACING THE FLOWABLE PORTIONS OF THE ADHESIVE LATERALLYBETWEEN SAID BACKING AND SAID FACING SHEET RADIALLY FROM THE AREAS OFAPPLIED PRESSURE; AND ACCUMULATING SAID PORTIONS OF THE ADHESIVE IN THELAYER AROUND THE AREAS OF APPLIED PRESSURE.